TheThe CameraCamera andand PhotographyPhotography

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science TypicalTypical ImagingImaging ChainChain forfor PhotographyPhotography

source (sun)

camera

processing object collection (lens) image exposure (aperture & shutter) detection (photographic film)

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science CollectionCollection

ν For a camera to be efficient, the pinhole is replaced by a lens. ν The lens redirects light rays emanating from the object.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science DepthDepth ofof FocusFocus:: TheThe rangerange ofof filmfilm locationslocations forfor whichwhich thethe photophoto ofof anan objectobject atat aa givengiven distancedistance comescomes outout acceptablyacceptably sharp.sharp.

DepthDepth ofof FieldField:: TheThe rangerange ofof objectobject distancesdistances thatthat resultresult inin anan acceptableacceptable photograph.photograph.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science ExposureExposure

camera Lens

Aperture Shutter

υ Exposure is defined as the total amount of light falling on the film. υ Exposure = Illuminance * Time

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science IlluminanceIlluminance

Small aperture Large aperture

υ Illuminance is the rate of light falling on a given area (i.e. energy per unit time). υ Illuminance is controlled by aperture: a larger aperture brings more light to the focus.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science ApertureAperture andand ““FF numbernumber””

d

υ F# (F number) is often used in photography to describe the aperture. υ F# = focal length of the system/diameter of aperture

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science ExposureExposure TimeTime

Shutter Closed Shutter Open

υ Exposure time is controlled by the shutter: when closed, the film is not exposed to light. υ Exposure time is simply the time interval between opening and closing the shutter.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science TypesTypes ofof ShuttersShutters

Simplified Camera

Between the Lens (BTL) Focal Plane Shutter Or Leaf Shutter

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science BTLBTL oror LeafLeaf ShutterShutter

υ Made of overlapping “leaves” that slide out of the way when CLOSED shutter opens. υ Located between the imaging lens elements.

OPEN

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science BTLBTL oror LeafLeaf ShutterShutter

υ Advantages υ Uniform illumination independent of film size. υ Entire film frame illuminated at once. υ Disadvantages υ Illumination of frame not constant over time. υ Limitations on shutter speed.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science FocalFocal PlanePlane ShutterShutter

υ Metal or fabric with a narrow slit opening which traverses the area to be exposed. υ Located just before the detector (film) at the focal plane.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science FocalFocal PlanePlane ShutterShutter

υ Advantages υ Cost effective (one shutter needed for all lenses - great for interchangeable lens systems) υ Can achieve very fast shutter speeds (~1/10000 sec) υ Disadvantages υ May cause time distortion if the film size is large (since the shutter slit must traverse the film) Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science WhyWhy controlcontrol exposureexposure withwith apertureaperture andand shutter?shutter?

υ Flexibility! υ Fast shutter speed for freezing action (e.g. sports photography). υ Slow shutter speed for low light levels (e.g. sunsets). υ Small aperture for bright scenes or to enable longer exposures. υ Large aperture for low light conditions (taking candle lit or moon lit pictures).

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science CaptureCapture

υ The image can now be captured using a detection system, such as photographic film. υ Film must be processed to yield a permanent, visible image.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science ImageImage CaptureCapture -- PhotographicPhotographic FilmFilm

υ Film consists of a photosensitive compound known as Silver Halide (AgX), which reacts with light. υ The area exposed to light turns dark after processing. υ The total amount of light hitting a given area of film (known as exposure) determines how dark that area turns.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science WhatWhat isis ““SilverSilver HalideHalide””??

υ Silver Halide is a compound made of silver (Ag) atoms and atoms from the halide group (Cl,Br,I) of the periodic table. υ The material property of a silver halide crystal changes after absorbing photons.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science SilverSilver andand halidehalide atomsatoms withinwithin thethe periodicperiodic tabletable ofof thethe elementselements

Silver (Ag)

Halide group

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science StructureStructure ofof aa TypicalTypical B&WB&W FilmFilm

υ Film base υ Plastic

υ Antihalation backing υ Prevents light from reflecting back. υ Emulsion Silver Halide Crystals Suspended in gelatin, like fruits in Jell-O™!

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science ExposedExposed AgXAgX CrystalsCrystals

hν υ When a silver halide crystal is exposed to Exposure light, some of the AgX molecules break up into their constituents, one of which is metallic silver (“pure” Ag). After Exposure

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science ProcessingProcessing PhotographicPhotographic FilmFilm

υ Turns latent image into visible image. υ Basic steps: υ Developer υ Stop bath υ Fix bath

υ All chemicals used in the process are in liquid form.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science SilverSilver HalideHalide ProcessProcess ChainChain

Exposure Processing Visible Latent Develop Stop Fix Image (Stable) Image

υ A latent image is formed after exposure (invisible to human eye). υ After processing, the latent image is turned into a visible, stable image.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science ProcessingProcessing PhotographicPhotographic FilmFilm

υ Developer “amplifies” the atomic silver to visible silver strands. υ Stop Bath stops the development process.

υ Fix dissolves the unexposed AgX crystals, making the film safe to expose to light.

υ Wash with water to rinse fix chemicals away.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science ““GrainGrain”” ofof FilmFilm andand PaperPaper

υ Electron Photomicrographs of Emulsion Grains υ (n.b. Measurement Bars indicate scale)

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science SilverSilver HalideHalide GrainsGrains

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science WhyWhy doesdoes processedprocessed filmfilm looklook ““negativenegative””??

υ Silver strands formed by exposure of photographic film to light actually appear dark (they are NOT shiny). υ So, where light hits the film during exposure, it turns darker.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science WhatWhat determinesdetermines howhow darkdark filmfilm becomes?becomes?

υ THE GRAINS! υ Size υ Shape υ Chemical composition υ Distribution

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science D-LogD-Log HH CurveCurve andand ContrastContrast

More contrast Less contrast

Image

Film D D response Log H Log H

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science PhotographicPhotographic FinishingFinishing

υ In order to get a “positive” final print, the negative must be projected onto photographic paper. υ Negative * negative = positive! υ 2 basic “finishing” methods: CONTACT and ENLARGEMENT/REDUCTION Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science ContactContact PrintingPrinting

Light

Negative Photographic Paper

A CONTACT print: The negative is in direct contact with the photographic paper --essentially creating a shadow-gram.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science EnlargerEnlarger // ReducerReducer

Light Negative

Photographic Paper

Optics are used to produce an image of the negative on photographic paper. Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science ContactContact PrintingPrinting vsvs.. EnlargerEnlarger

Contact Printing Enlarger

υ No loss of signal by υ Flexible image size. the optics. υ Some loss in υ No reduction in resolution due to resolution. enlargement. υ Simpler system. υ Additional optics υ Fixed image size. may degrade final image quality. υ Again, flexibility!

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science LatentLatent ImageImage FormationFormation (Ex.:(Ex.: shadowgramshadowgram))

• Group of AgX Crystals

• Mask (object) prevents AgX crystals underneath to be exposed. • “Unmasked” AgX is exposed to photons. • Exposed crystals have different material property (I.e. some AgX bonds have been broken). Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science LatentLatent ImageImage FormationFormation (with(with optics)optics)

• Group of AgX Crystals

• Optics used to image object onto the film.

•Illuminated AgX is exposed to photons; but not all AgX is illuminated.

• Exposed crystals have a different material property.

Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science